What is a good annual salary?
One that is at once high enough to make you happy to go to work, and low enough for your employer to be able to keep you as a worker.
The "mean annual salary" is the average salary being paid for a job or position. Your annual salary is the amount that you will get paid in a year assuming you work the entire year at that salary. For example, if you are paid semi-monthly (such as US military pay, 1st and 15th of each month), and your annual salary is $24,000, your gross paycheck (before taxes) will be $2,000.
It all depends on what inventor you are talking about. In most cases, inventors get money for products they make so it then varies from how good their product is. So there is no real annual salary of an inventor but if you worked out the average income of a good inventor over a decade you'll get around +$120,000US a year.